Pretuning V1 (S7-1200, S7-1500) - PID

Using PID_Compact (S7-1200, S7-1500)
ft:publication_title
Using PID_Compact (S7-1200, S7-1500)
Product
PID
Version
V20
Publication date
11/2024
Language
en-US
Pretuning V1

The pretuning determines the process response to a jump change of the output value and searches for the point of inflection. The tuned PID parameters are calculated as a function of the maximum slope and dead time of the controlled system.

The more stable the process value is, the easier it is to calculate the PID parameters and the more precise the result will be. Noise on the process value can be tolerated as long as the rate of rise of the process value is significantly higher compared to the noise. The PID parameters are backed up before being recalculated.

Requirement

  • The "PID_Compact" instruction is called in a cyclic interrupt OB.

  • ManualEnable = FALSE

  • PID_Compact is in "inactive" or "manual" mode.

  • The setpoint may not be changed during controller tuning. PID_Compact will otherwise be deactivated.

  • The setpoint and the process value lie within the configured limits (see "Process value monitoring" configuration).

  • The difference between setpoint and process value is greater than 30% of the difference between process value high limit and process value low limit.

  • The distance between the setpoint and the process value is > 50% of the setpoint.

Procedure

To perform pretuning, follow these steps:

  1. Double-click the "PID_Compact > Commissioning" entry in the project tree.

  2. Select the entry "Pretuning" in the "Tuning mode" drop-down list.

  3. Click the "Start" icon.

    • An online connection will be established.

    • Value recording is started.

    • Pretuning is started.

    • The "Status" field displays the current steps and any errors that may have occurred. The progress bar indicates the progress of the current step.

      Note

      Click the "Stop" icon when the progress bar has reached 100% and it is to be assumed the controller tuning function is blocked. Check the configuration of the technology object and, if necessary, restart controller tuning.

Result

If pretuning was performed without an error message, the PID parameters have been tuned. PID_Compact switches to automatic mode and uses the tuned parameters. The tuned PID parameters will be retained during power OFF and a restart of the CPU.

If pretuning is not possible, PID_Compact will change to "Inactive" mode.